Echo reduction for a headset or handset

ABSTRACT

The present invention provides an echo reduction apparatus, system, and method that advantageously reduces echo when communicating over packet-switched networks. An echo reduction apparatus, including echo reduction circuit, operably couples a headset or handset device to an audio source that is capable of transmitting a sound signal. The echo reduction circuit receives the sound signal from the audio source and a transmit signal from the headset or handset device and provides an adjusted sound signal to the audio source. Advantageously, a variety of headsets and handsets may be used in accordance with the present invention with reduced caller echo and without the need to purchase new headsets or handsets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.10/256,450, filed Sep. 27, 2002, now U.S. Pat. No. 7,039,179 which isincorporated by reference herein for all purposes.

BACKGROUND

1. Field of the Invention

This invention generally relates to an apparatus, system, and method forimproved telephony and, more particularly, to an apparatus, system, andmethod for reducing or eliminating echo when communicating overpacket-switched telephone connections.

2. Description of Related Art

Digital circuit switches have traditionally been used to route voicetraffic and low-throughput data traffic but advances in electronics havemade packet-switched digital connections, such as Voice over InternetProtocol, increasingly cost-effective.

Circuit switches traditionally provided a physical, dedicated path,called a time slot, for a call when it went through the switchingmatrix. Because this path was dedicated to the call, no other callerscould use the selected switch path until the call ended. This concept ofa dedicated path guaranteed high-quality, almost error-free transmissionfor the call.

Packet switches, in contrast, do not use dedicated paths, but evolved inthe 1970s to handle the variable bit rates of data transmission bursts.Packet switches take a user's data stream, break it down into smallersegments, called packets, add network control information, and thentransmit the packets through the network in bursts. When a burst of datacomes in, switching resources are assigned for that burst, with theresources being shared on an as-needed, first-come, first-served basis.At the end of the burst of data, the resources are available for thenext burst of data.

The steady rise in signal processing power, memory capacity, operatingspeed, and error correction has allowed packet-switched networks tohandle the real-time demands of voice traffic. With the huge increase ofInternet users and data transmissions over communication networks in thepast several years, telecommunication companies and Internet providersare moving to route both voice and data traffic, as well as Internettraffic, over packet-switched networks.

A disadvantage of packet-switched networks has been that the amount ofreal-time processing required to control the packets has been enormous.Accordingly, the real-time processing has introduced a certain amount ofdelay in moving a packet through the network. Thus, packet-switchedconnections necessarily add a perceptible amount of delay to signaltransmission, while traditional circuit-switched connections do notcreate perceptible delay since a path remains fixed once a call is setup. This delay makes objectionable even a small amount of coupling ofthe received voice signal into the transmitted signal, which causes acaller to hear an echo of his/her own voice. Most callers find such anecho, even one that is not loud, to be distracting and annoying.

Telephone headsets commonly couple more of the received signal into thetransmitted signal than is optimal for modern, packet-switchedconnections. Similarly, many handsets in use today were not designedwith the requirements of packet-switched telephony in mind, andtherefore couple more of the received signal into the transmitted signalthan is optimal.

Different methods have been used to reduce echo associated withtelephones. One method has been to change the mechanical and acousticcharacteristics of the headset to reduce coupling between the receivesignal and the transmit signal. Disadvantageously, this method requirescompromising other desirable characteristics of the headset, such aswearing comfort, weight, small size, and low cost. Furthermore, thismethod requires the owner of an existing headset to purchase a new one.

A second method has been to suppress undesired echoes using equipment orsoftware within the telephone network between the telephones in use.This method has included either digital hardware or digital signalprocessing software built into the network equipment to help solve thefundamental delay problems for stream voice, video, or raw data.Unfortunately, network echo reduction equipment is commonly optimizedfor handling echoes that originate within the network, whosecharacteristics remain relatively constant for the duration of a singlecall. However, the undesired signal coupling in a headset or handset canvary rapidly during a call, since small movements of the user can affectthe coupling. This rapid variation greatly reduces the effectiveness ofnetwork echo reduction equipment. Accordingly, such network equipmentcannot accommodate the complex characteristics of the adjuncts connectedto the user side of these gateways or packet-switched networks.

A third method has been to suppress undesired echoes using equipmentdesigned into the telephone itself. However, many phones in use todaylack such means to reduce the echo caused by undesired coupling.Furthermore, when the user attempts to use a telephone headset or atelephone handset which is different from that provided with thetelephone originally, the caller can hear undesirable echo.

Therefore, there is a need for an apparatus, system, and method thatallows for a reduction in echo when using a variety of headsets andhandsets in conjunction with packet-switched networks without having topurchase new headsets or handsets.

The present invention provides echo reduction circuit between a headsetor handset device and an audio source to advantageously reduce orsuppress caller echo associated with packet-switched networks.

In one embodiment of the present invention, an echo reduction apparatusis provided, comprising a first connection interface capable of operablycoupling a headset or handset device to the echo reduction apparatus, asecond connection interface capable of operably coupling an externalaudio source to the echo reduction apparatus, and an echo reductioncircuit operably coupled to the first and second connection interfaces.The echo reduction circuit is capable of receiving a sound signal fromthe audio source, comparing the sound signal from the audio source to asound signal from the headset or handset device, and providing anadjusted sound signal to the audio source.

In another embodiment of the present invention, an echo reduction systemis provided, comprising an audio source that is capable of transmittinga sound signal, a headset or handset device operably coupled to theaudio source, wherein the headset or handset device is capable oftransmitting a sound signal, and an echo reduction apparatus operablycoupled between the audio source and the headset or handset device.

In yet another embodiment of the present invention, a method of reducingecho is provided, comprising providing an echo reduction circuitoperably coupled between a headset or handset device and an audiosource, transmitting a sound signal from the audio source to the echoreduction circuit, comparing the sound signal from the audio source to asound signal from the headset or handset device, adjusting the soundsignal from the headset or handset device as necessary, and transmittingthe adjusted sound signal to the audio source.

Advantageously, the present invention allows for a reduction in echowhen using headsets and handsets that do not meet the stringentreceive-transmit coupling requirements of packet-switched telephony.

These and other features and advantages of the present invention will bemore readily apparent from the detailed description of the embodimentsset forth below taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an echo reduction system in accordancewith an embodiment of the present invention.

FIG. 2 shows a block diagram of an echo reduction system applied in adetailed example of an end-to-end communication system, in accordancewith another embodiment of the present invention.

FIG. 3A shows a block diagram of an echo reduction apparatus includingone example of echo reduction circuit in accordance with an embodimentof the present invention.

FIG. 3B shows a block diagram of an echo reduction apparatus includinganother example of echo reduction circuit in accordance with anembodiment of the present invention.

Use of the same reference symbols in different figures indicates similaror identical items.

DETAILED DESCRIPTION

The present invention provides an echo reduction apparatus, includingecho suppression or cancellation circuit operably connected to a headsetor handset device to advantageously reduce or prevent caller echo thatwould otherwise occur through a packet-switched network (e.g., theInternet).

FIG. 1 shows a simplified block diagram of an echo reduction system 100in accordance with one embodiment of the present invention. In thisembodiment, an audio source 106 is operably connected to an echoreduction apparatus 104, which receives an input audio signal along lead105 from audio source 106. The present invention is not limited to aspecific audio source 106 and may receive an audio signal from anyapplicable audio signal source, for example, a communications network, acomputer, a telephone, a cellular telephone, or any other host telephonyapparatus. As an example, with no intent to limit the invention thereby,a communications network may include a public switched telephone network(PSTN), an integrated services digital network (ISDN), a local areanetwork (LAN), and/or a wireless local area network (WLAN), withstandards such as Ethernet, wireless fidelity (WiFi), and/or voice overinternet protocol (VOIP).

An audio input/output device 102 is also operably connected to echoreduction apparatus 104 via lead 103. Audio input/output device 102includes speaker (or earphone) and microphone transducers and is capableof sending a sound signal to echo reduction apparatus 104 along lead103. It is noted that echo reduction apparatus 104 may be added inplurality to match any number of earphones and associated leakage paths.It is further noted that audio input/output device 102 may also includemultiple microphones, and in such a situation, a plurality of echoreduction apparatus 104 could also be beneficial.

Echo reduction apparatus 104 includes echo suppression and/orcancellation circuit in one embodiment that receives signals from audiosource 106 and from audio input/output device 102, compares the signals,and provides an adjusted signal to audio source 106 in order to reduceor cancel echo.

Echo reduction apparatus 104 also acts as an adapter to enablecompatibility between audio source 106 and audio input/output device102, such as a headset or handset device. In one example, echo reductionapparatus 104 includes connection interfaces 108 and 110 to allow foroperable coupling between audio source 106 and echo reduction apparatus104 and between echo reduction apparatus 104 and audio input/outputdevice 102, respectively, thereby allowing for operable coupling betweenaudio source 106 and audio input/output device 102. Connectioninterfaces 108 and 110 may include plugs, headset or handset jacks,cables, cords, and any other applicable connecting or adaptive means inaccordance with the present invention. It is noted that echo reductionapparatus 104 may act as an adapter to fit a wide range of headset orhandset device and/or a wide range of audio sources. An example of astructure suitable for use in the present invention, with no intent tolimit the invention thereby, is Vista™ Universal Amplifier Model M12,available from Plantronics®, Inc., located in Santa Cruz, Calif.

FIG. 2 shows a detailed block diagram of an echo reduction system 200 inan example of a complete end-to-end telecommunication application, inaccordance with another embodiment of the present invention. Anexemplary embodiment of audio input/output device 102 is a headset orhandset device 202 that includes an earphone transducer and a microphonetransducer. Headset or handset device 202 converts the received audiosignal from audio source 106 to an acoustic signal to be heard by theheadset or handset device user. Any signal leakage; either internal orexternal to headset or handset device 202, is represented by leakagepath 201. Leakage path 201 represents earphone activity (acoustic and/orelectro-mechanical) that is undesirably coupled to the microphone andtransmitted from headset or handset device 202. It is noted that theuser's face, ears, and/or mouth can interact with the headset/handsetapparatus to modify the magnitude and frequency response of the unwantedleakage signal, whether purely acoustic, electro-mechanical, or acombination of both.

As noted above, several different versions of headset or handset device202 may be used in conjunction with echo reduction apparatus 104 to givethe user a choice of headset or handset device to wear or use. Headsetor handset device 202 can include any adaptable headset apparatus suchas the Encore™ series commercially available from Plantronics®, Inc.,located in Santa Cruz, Calif.

Typically, leads 103 and 105 (FIG. 1) are analog in nature and require 4wires: 2 wires for the receive signal paths and 2 wires for the transmitsignal paths, as shown in FIG. 2. In accordance with one embodiment ofthe present invention, headset or handset device 202 is operablyconnected to echo reduction apparatus 104 including echo reductioncircuit 204, as illustrated in FIG. 2. A user interface 218 may also beoptionally included with echo reduction apparatus 104 and specificallyis connected to gain circuit 216 through lead 217. User interface 218allows the user to manually adjust the gain of the receive signal beingheard through headset or handset device 202.

Echo reduction circuit 204 is operably connected to audio source 106,such as a host telephony system, as shown in FIG. 2. In this example,audio source 106 is comprised of a headset/handset interface 206, suchas a telephone or communication terminal, a packet-switched network 210including gateways 210 a and 210 c and pathway 210 b, a phone interface212, and a telephone 214. Many other combinations of telephonetechnology may be involved at either end of the telecommunication linkshown in FIG. 2, but common elements will involve packet-switchednetwork 210, which are the gateways and pathways that join digitaland/or analog (e.g., PSTN) telephone systems together.

Accordingly, the far end user of telephone 214 can experience an echo ofhis/her own voice delayed in time, the severity of which is dictated bythe acoustic and mechanical isolation limitations of headset or handsetdevice 202 (i.e., the signal leakage path 201), overall network signalgain, and the total amount of fixed and/or varying packet switchingdelay through network 210. Advantageously, echo reduction apparatus 104reduces this echo by utilizing echo reduction circuit between headset orhandset device 202 and audio source 106, as described in greater detailbelow.

FIG. 3A shows a block diagram of some of the electrical components thatare included in one example of echo reduction circuit 204. In oneexample of a receive path from audio source 106 (FIGS. 1 and 2), echoreduction circuit 204 may include an analog-to-digital (A/D) converter302 a to receive an analog input audio signal along lead 105 a fromaudio source 106 (FIG. 1). A/D converter 302 a converts the signal intoa digital signal for processing by digital signal processor (DSP) 300.A/D converter 302 a may be any suitable means for decoding anddigitizing analog audio signals.

As further shown in FIG. 3A, the digital signal from DSP 300 may be sentto a digital-to-analog (D/A) converter 301 a for conversion of thedigital signal to an analog signal. D/A converter 301 a may be anysuitable device for converting digital audio signals to analog audiosignals. Finally, the analog signal is sent along lead 103 a to headsetor handset device 202 (FIG. 2), where it is converted into an acousticsignal which is heard by the user.

Alternatively, since the incoming receive signal needs only to bemonitored or sampled by the processor, A/D converter 302 a can monitorthe receive signal along lead 105 a, and lead 303 (shown by dashedlines) could be used to bypass any conversion and signal processing onthe receive signal. Thus, D/A converter 301 a could be omitted in thisexample.

Similarly, in another embodiment, headset or handset device 202 (FIG. 2)may receive digital signals. After DSP 300 samples the digitized inputsignal, or the digital signal is directly sent to headset or handsetdevice 202 (FIG. 2), the digital signal may be converted into anacoustic signal by headset or handset device 202 (FIG. 2) which is heardby the user. Again, D/A converter 301 a may be omitted in thisembodiment.

In an example of a transmit path from headset or handset device 202(FIG. 2), echo reduction circuit 204 may include an analog-to-digital(A/D) converter 301 b to receive an analog audio signal along lead 103 bfrom headset or handset device 202 (FIG. 2). A/D converter 301 b may beany suitable means for decoding and digitizing analog audio signals. A/Dconverter 301 b converts the signal into a digital signal for deliveryto the digital input of DSP 300.

DSP 300 separates the transmit signal (including undesirable leakagesignal from insufficient isolation between the earphone and microphoneand delay from the packet-switched network) into elements that can becompared with the monitored receive signal delivered to DSP 300 from A/Dconverter 302 a. If measured amounts of receive signal are detected inthe transmit signal, then a DSP algorithm will create a correctionsignal (anti-signal) to remove the detected receive signal from thetransmit signal.

Transfer functions, either specific to audio input/output device 102(FIG. 1) or more generally applicable, may be used to provide frequencyand level adjustments to best represent the leakage path characteristicsof the audio input/output device 102 (FIG. 1), thereby optimizingdetermination of the anti-signal to achieve optimum echo reduction.Optionally, table readouts of the transfer function between electricalsignal received by the earphone and leakage signal transmitted throughthe microphone for the range of adaptable headsets or handsets may beused to modify the correction signal. In one example, transfer functionsmay be determined using laboratory telephone headsets or handsets tomonitor signal leakage over frequency and gain.

It is noted that various techniques have been proposed and implementedwith telephones and speakerphones in order to address the problem ofechoes due to acoustic coupling. These techniques generally fall intocategories of echo suppression and echo cancellation. Echo cancellationtypically involves calculating an estimated echo signal from the speakeroutput signal and subtracting the estimated echo signal from themicrophone transmit signal, thus generating a corrected transmit signal.Echo suppression, on the other hand, typically involves operating thetelephone in half-duplex mode wherein only one path (the receive path orthe transmit path) is open at any one time. It is also known to operatethe telephone in a quasi-half duplex mode in which neither path is fullyclosed, but one path may be attenuated more than the other path at anygive time. Various forms of DSP echo cancellation and/or suppressionalgorithms may be used in accordance with the present invention, as willbe evident to those of ordinary skill in the art.

Referring again to FIG. 3A, the adjusted digital signal from DSP 300 isthen sent to digital-to-analog (D/A) converter 302 b for conversion ofthe digital signal to an analog signal. D/A converter 302 b may be anysuitable device for converting digital audio signals to analog audiosignals. It is noted that A/D converter 302 a and D/A converter 302 bneed not be separate devices but may be combined into a singlestructure. Similarly, it is noted that D/A converter 301 a and A/Dconverter 301 b need not be separate devices but may be combined into asingle structure. Finally, the analog signal is sent along lead 105 b toaudio source 106 (FIGS. 1 and 2) with reduced echo.

FIG. 3B illustrates another example of echo reduction circuit 204 thatmay be used in accordance with the present invention to reduce oreliminate echo while communicating through a headset or handsetapparatus. In this example, echo reduction circuit 204 includes analogsignal processing blocks. Advantageously, this example does not requireconversion to the digital domain and thereby eliminates the additionalsignal delays caused by analog and digital conversions and by theprocessing latency associated with the DSP. However, this example is notas easily adaptable or programmable in reducing echo as the previouslydescribed example illustrated in FIG. 3A.

Referring again to FIG. 3B, a signal is received from audio source 106(FIGS. 1 and 2) along lead 105 a and sent to headset or handset device202 (FIG. 2) along lead 103 a. A frequency difference amplifier 304receives the receive signal along lead 303 and the transmit signal fromheadset or handset device 202 (FIG. 2) along lead 311. Frequencydifference amplifier 304 provides a comparison of the receive andtransmit signals. If the transmit signal matches some of the receivesignal, frequency difference amplifier 304 provides a control signalalong lead 313 to enable a voltage controlled amplifier (VCA) 306. VCA306 produces a limited amount of receive signal along lead 307 to beused as a correction signal.

The limited amount of receive signal from VCA 306 is modified by atransfer function 308 either specific to headset or handset device 202or more generally applicable to a group of headset or handset devices.Transfer function 308 provides frequency and level adjustments to bestrepresent the leakage path characteristics of headset or handset device202 (FIG. 2) and may be applied by software or hardware. Optionally,table readouts of the transfer function between electrical signalreceived by the earphone and leakage signal transmitted through themicrophone for the range of adaptable headsets or handsets may be usedto modify the correction signal. In one example, transfer function 308may be determined using laboratory telephone headsets or handsets tomonitor signal leakage over frequency and gain.

The resulting correction signal is sent along lead 309 to asum/difference amplifier 310 where the correction signal is subtractedfrom the transmit signal sent to sum/difference amplifier 310 along lead315. The resulting output of sum/difference amplifier 310 is sent alonglead 105 b to audio source 106 (FIGS. 1 and 2) as an echo-reducedtransmit signal from headset or handset device 202. It is again notedthat various forms of analog design and signal processing may be used,as will be evident to those of ordinary skill in the art. Furthermore,it is noted that if the human interface to audio input/output device 102(FIG. 1) dramatically changes the transfer function of audioinput/output device 102 (FIG. 1) in real-time, then the lack of analogadaptability may limit the available range of echo reduction in thisexample.

Although in the previous embodiments, a separate echo reductionapparatus 204 has been described, the invention is not limited to aseparate apparatus. It will be apparent to those of ordinary skill inthe art that the previously described echo reduction circuit, adaptivefeatures, and user interface of echo reduction apparatus 204 may beincorporated into headset/handset 202 to effectively reduce echo.

Furthermore, while communication channels within FIGS. 1-3B have beenreferred to as leads, it should be understood that what are called leadscan be buses capable of carrying a plurality of signals (either digitalor analog as appropriate) in parallel or can even be wirelesscommunication channels.

The above-described embodiments of the present invention are merelymeant to be illustrative and not limiting. It will thus be obvious tothose skilled in the art that various changes and modifications may bemade without departing from this invention in its broader aspects.Therefore, the appended claims encompass all such changes andmodifications as falling within the true spirit and scope of thisinvention.

1. An echo reduction apparatus, comprising: a first connection interfacecapable of operably coupling an audio input/output device; a secondconnection interface capable of operably coupling an external audiosource; and an echo reduction circuit operably coupled to the first andsecond connection interfaces, wherein the echo reduction circuitincludes a transfer function representing signal leakage characteristicsspecific to the audio input/output device, and further wherein the echoreduction circuit is capable of using the transfer function to providean adjusted sound signal to the audio source for reducing echo.
 2. Theapparatus of claim 1, wherein the audio input/output device is externalto the echo reduction apparatus.
 3. The apparatus of claim 1, whereinthe first connection interface is capable of operably coupling differentheadset or handset devices to the echo reduction circuit.
 4. Theapparatus of claim 1, wherein the audio source is selected from thegroup consisting of a communications network, a computer, a telephone,and a cellular telephone.
 5. The apparatus of claim 1, wherein the soundsignal from the audio source is delayed through a packet-switchednetwork prior to being received by the echo reduction circuit.
 6. Theapparatus of claim 1, wherein the echo reduction circuit comprises adigital signal processor.
 7. The apparatus of claim 1, wherein the echoreduction circuit comprises an analog-to-digital converter or adigital-to-analog converter.
 8. The apparatus of claim 1, furthercomprising a gain control circuit operably coupled to the first andsecond connection interfaces.
 9. The apparatus of claim 8, furthercomprising a user interface operably coupled to the gain control circuitto allow for volume control of the sound signal from the audio source.10. An echo reduction system, comprising: an audio source that iscapable of transmitting a sound signal; an audio input/output deviceoperably coupled to the audio source, wherein the audio input/outputdevice is capable of transmitting a sound signal; and an echo reductionapparatus operably coupled between the audio source and the audioinput/output device, wherein the echo reduction apparatus comprises anecho reduction circuit including a transfer function representing signalleakage characteristics specific to the audio input/output device, theecho reduction circuit capable of using the transfer function to providean adjusted sound signal to the audio source for reducing echo.
 11. Thesystem of claim 10, wherein the echo reduction apparatus is external tothe audio source.
 12. The system of claim 10, wherein the audio sourceis selected from the group consisting of a communications network, acomputer, a telephone, and a cellular telephone.
 13. The system of claim10, wherein the sound signal transmitted from the audio source isdelayed through a packet-switched network prior to being received by theecho reduction circuit.
 14. The system of claim 10, wherein the audioinput/output device may be selected from a plurality of headset orhandset devices.
 15. The system of claim 10, wherein the echo reductionapparatus further comprises a user interface to allow for volume controlof the sound signal.
 16. A method of reducing echo, comprising:providing an echo reduction circuit operably coupled between an audioinput/output device and an audio source; adjusting a sound signal fromthe audio input/output device as necessary, wherein the sound signal isadjusted by a transfer function representing signal leakagecharacteristics specific to the audio input/output device; andtransmitting the adjusted sound signal to the audio source.
 17. Themethod of claim 16, wherein the sound signal from the audio source isdelayed through a packet-switched network prior to being received by theecho reduction circuit.
 18. The method of claim 16, wherein the audioinput/output device may be selected from a plurality of headset orhandset devices.
 19. The method of claim 16, further comprisingcomparing the sound signal from the audio source to the sound signalfrom the audio input/output device by a digital signal processor.